The present invention relates generally to photodiode detector means for producing a plurality of signal outputs when activated by the impingement of optical radiation. More specifically, the invention relates to photo electric lightning detectors using single-axis photodiodes to monitor lightning discharges.
Present methods for locating lightning discharges are based on detecting electromagnetic field or optical transients produced by the discharge. Crossed-loop direction finders and other versions of sferic detectors are in common use as are cameras and T.V. systems. Unfortunately, the complex nature of the emitting source and the rather long wavelengths involved limit the accuracy of the electronic field techniques. Photography can provide accurate angular information but, again, it is limited in time resolution and in the rather slow processing of the data. Additionally, photography suffers during daylight because of film exposure. Sophisticated T.V. systems with video recording have fair accuracy and time-resolution but can become rather expensive and cumbersome particularly when used in field experiments.
Usually, systems of these various types are employed for the purpose of accurately determining the actual location of lightning strokes under study. However, in other situations, such as those presently contemplated, it becomes highly desirable to monitor some object or location to determine whether a lightning discharge has occurred in its vicinity and, if so, the proximity of the discharge to the object. For example, it is quite desirable to monitor large rocket launch towers because, obviously, such towers may well be detrimentally affected by lightning and, if so, immediate repairs must be made. Other targets such as satellites, or flammable targets such as oil tanks or forests are vulnerable to lightning discharges so as to benefit by constant monitoring. However, acceptable monitoring of these objects should be accomplished in real time and also with a highly precise angular resolution. As already indicated, present methods are especially deficient in these regards.
It is recognized that photodiode detectors of the type generally under consideration are known devices and, further, that they have been used in conjunction with a focusing lens to locate or determine the position of a source of light. For example, U.S. Pat. No. 3,800,146 issued Mar. 26, 1974 to Brunkhorst, Carr and Dueker describes these light sensitive detectors in some detail and further identifies other U.S. Patents in which the detectors are disclosed. These detectors, however, mostly are of a type producing quadrature outputs as opposed to the single-axis detector presently used.